Method for machining opening in workpieces

ABSTRACT

A procedure to machine openings in work pieces proposes to position two cutting blades ( 11, 12 ) of a cutting tool ( 2 ) with an axis of rotation ( 15 ) alongside a cutting blade axis at a distance to one another, which is greater than the required distance between two oppositely positioned opening edges to be machined ( 6, 7 ) alongside an opening axis ( 9 ), which runs through these opening edges. The opening axis and the cutting blade axis are inclined at an acute angle (α) to one another in a way that the distance of the cutting blades to the opening axis ( 9 ) is equal to the required distance between the opening edges. With the increasing wear of the cutting blades the inclination angle is reduced so that the cutting blade distance parallel to the opening axis continues to correspond to the required distance of the opening edges.

BACKGROUND OF THE INVENTION

[0001] 1. Field of Invention

[0002] The invention refers to a procedure for machining openings inwork pieces, in particular windows in ball cages for constant velocityjoints.

[0003] 2. Description of the Prior Art

[0004] In almost every passenger vehicle two constant velocity jointsare required. In the production of these constant velocity joints, twowindows with very exact tolerances have to be introduced intro ballcages. The dimension has to be controlled to {fraction (1/1000)} mm toensure guiding of the balls free of play. Typically, the windows of theball cages are first punched and then finished with a single-toothmilling cutter, which sits on a powered shaft. The cutting blade weararising in this procedure is a factor that cannot be neglected.

[0005] EP 0 952 364 A1 describes such a procedure to finish the windowsof ball cages. To maintain the exact dimension for the height and thewidth of a window in such a procedure, typically one edge of a window ismachined first with one cutting blade and then the opposite edge of thewindow is machined with the opposite cutting blade. Here, the tool'swear is balanced by measuring the window dimension again and, if itshows that the tolerances are likely to be exceeded, the position of therespective cutting blade is moved to the respective limit of thetolerance area. This way it is possible to maintain the very narrowtolerances on the window dimensions in spite of tool wear. Adisadvantage of such a procedure is that the machining time isrelatively long. It is know from EP 0 952 364 A1 that two opposingwindow opening edges can be machined simultaneously with one tool, whichleads to a reduction of the machining time. In this document, however,no hint is given as to how the narrow tolerance requirements can be metwith the occurring wear of the tool over the lifetime of the tool.

[0006] In contrast to this, the purpose of this invention is to improvea procedure of the kind mentioned in the beginning that maintains a highdimensional accuracy and reduces the time to manufacture openings inwork pieces.

[0007] According to the invention, such a task is successfully carriedout in this kind of procedure by the following steps: Positioning of thetwo cutting blades alongside the cutting blade axis at a distance fromeach other, which is greater than the required distance of the openingedges; inclining the imagined opening axis and the cutting blade axis inan initial state at an acute angle to each other so that the effectivedistance between the cutting blades defined along a line parallel to theopening axis is equal to the required distance of the opening edges, andreduction of the inclination angle with increasing wear of the cuttingblades so that the cutting blade distance parallel to the opening axiscontinues to correspond to the required distance between the openingedges.

[0008] In another aspect, the present invention is defined by the stepsof: providing a cutting tool, which rotates around an axis of rotation,having two cutting blades positioned alongside the axis of rotation anddefining a distance between them along an axis running through bothblades; supporting a work piece near the cutting tool and defining anopening axis running through two oppositely positioned opening edges tobe machined therein, providing the opening axis at a predeterminedangular alignment relative to the cutting blade axis, and machining theopening edges in the work piece by cutting one opening edge with onecutting blade and the other opening edge with the other cutting blade,forming the opening edges at a required dimension from one another asdefined along the opening axis.

[0009] According to the method of the invention, openings in work piecescan be machined in one machining operation, i.e., in only one step andthus the machining times can be cut in half without affecting themachining accuracy. Since the cutting blade axis is inclined to thecentral axis of the opening to be manufactured and this inclination isreduced with increasing wear of the cutting blades, the reduction of thewear-related cutting blade distance is compensated for and thus therequired distance of the opening edges is maintained. According to theinvention, wear of both cutting blades is therefore simultaneouslycompensated for. Thus, the ball cage window width is manufactured in onestep; where the window width is maintained constant over the lifetime ofthe tool, that is to say, in spite of tool wear. In doing so, thecutting tool can be swung around a fixed point relative to the imaginedwindow axis.

[0010] The invention is preferably used to finish or rework openingsthat have been manufactured in previous work steps, although the termmachining of the opening edges may also comprise complete manufacturingof an opening in a work piece.

[0011] Preferably, within the framework of the invention, the openingaxis and the cutting blade axis are in an initial position inclinedrelative to one another by an included angle of approximately 5°. Forangles above a maximum of about 5°, the difference in machining depthdue to the inclination at the two oppositely positioned opening edges isso small, especially with windows in ball cages for constant velocityjoints, that in practice it can be neglected.

[0012] According to the invention, as the cutting blades wear theinclination angle from the initial position of about 5° is reduced toabout 0°, with the cutting blades being totally worn at about 0°. Withthese measures, the cutting tool—avoiding too great an initialinclination, which is not desired in production technology—is usedoptimally. Additionally, the level of wear can also be read from theinclination.

[0013] According to the invention, the inclination angle of the cuttingblade axis is adjusted into an initial position and thereafter theinclination angle is reduced. In doing so, especially the cutting bladeaxis and the axis of rotation should be rigidly joined. To position andreduce the inclination angle, the inclination of the axis of rotation isadjusted. Preferably, the cutting blade axis is placed parallel to theaxis of rotation of the cutting tool. In the framework of the invention,however, the cutting blade axis may also be defined so as to be notparallel to the axis of rotation.

[0014] According to the invention, definition and reduction of theinclination angle may also be achieved by modifying the inclination ofthe work piece with the inclination of the cutting blade axisalternatively held constant or also simultaneously be adjusted.

[0015] With the measures indicated above, the CNC technology can beoptimally used according to the existing current conditions.

[0016] According to the invention, the work piece is put into motion inthe same direction of rotation as the cutting tool so that the surfaceof circumference of the work piece and the cutting blades are moved inopposite directions at contact and the cutting blades machine thesurface openings along the circumference at regular intervals.Therefore, the work piece, in particular a ball cage for constantvelocity joints, is completely finished in one work step and in a simpleway, as far as openings or windows are concerned. In addition to theabove described opposite movements there is also the possibility for asynchronous rotation.

[0017] Alternatively, machining can also be done with a work piece thatis fixedly held during machining of an individual opening. Afterfinishing or completing machining of the individual openings, the workpiece is brought into a position that allows machining of the nextopening.

[0018] According to the invention, it may be desirable at the end of amachining process to increase the inclination angle in such a way thatthe forming of grooves in the opening edges, due to a subsequent pullingout or retraction of the cutting tool from the opening, is prevented. Ifthe inclination angle were not to be increased and the work piece ispulled out or retracted in a direction normal to the machined work piecesurface, undesired grooves would appear at least at one opening edge dueto the inclination.

[0019] However, by a generally minimal increase of the inclinationangles and the thus reduced actual width of the cutting tool, thiseffect can be avoided. To machine the next opening, the mentioned anglemodification is canceled if not angle modifications are necessary tocompensate for the wear effects.

[0020] Alternatively, retraction grooves may be avoided by stoppingrotation of the tool before turning the work piece to machine the nextopening. Therefore, removal of the work piece is possible without anygrooves appearing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The invention is explained in more detail by the followingdrawing. It is shown:

[0022]FIG. 1 Is a schematic representation of a cross section of a workpiece, more specifically, a ball cage for constant velocity joints, anda cutting tool, which according to the invented procedure are in aninclined position facing each other;

[0023]FIG. 2 is a schematic representation of a cutting tool, atriangular cutting plates in an initial position, in which the cuttingblade axis is inclined at an angle to the vertical, and in a finalposition, in which the cutting blade is completely worn and theinclination angle reduced to 0°; and

[0024]FIG. 3 is a schematic representation of a second applicationexample of the procedure according to the invention in which the openingaxis is inclined to the vertical.

DETAILED DESCRIPTION OF THE INVENTION

[0025]FIG. 1 shows a work piece, in this embodiment a ball cage 1 forconstant velocity joints, in which window edges 6, 7 are to be machinedwith a cutting tool 2. The example shows a triangular shapedsingle-tooth milling cutter.

[0026] The shown ball cage 1 in the example is formed rotationallysymmetric with an axis of rotation or longitudinal axis 4 and a bowshaped circumferential wall 5, which is bulging out towards the exteriorand whose summit is in the middle of its longitudinal extension. In theball cage 1 there are supposed to be finished window edges 6, 7, atregular intervals in the circumferential direction, which are shown inFIG. 1 with their finished dimensions. The upper and lower window edges6, 7 are running in the direction of the thickness of thecircumferential wall 5 at a right angle to the longitudinal axis 4 ofthe ball cage 1 and shows a mutual required distance 8, parallel to animagined window axis 9, running through them. The imagined window axis 9runs through the center of the thickness or horizontal extension of thewindow edges 6, 7, respectively, and, in the example shown in FIG. 1,parallel to the longitudinal axis 4 of the ball cage 1.

[0027] The cutting tool in the example shown is a triangularsingle-tooth milling cutter 2, which is attached to a shaft 10 of a CNCmachine tool. The cutting plate of the single tooth milling cutter 2shows two cutting edges or blades 11, 12, which define a cutting bladeaxis 13 running through both. The upper cutting blase 11 of FIG. 1serves for machining the upper window edge 6 and the lower cutting blade12 is for machining the lower window edge 7. Measured along the cuttingblade axis 13, both cutting blades 11, 12 are positioned with a distance14 from each other. This distance 14 is greater than the distance 8 ofthe window edges 6, 7 to be machined along the window axis 9. In theexample shown, the cutting blade axis 13 runs parallel to the axis ofrotation 15 of the machine tool shaft 10.

[0028] To machine the window edges 6, 7, the longitudinal axis 4 of theball cage 1 or, respectively, the window axis 9 and the cutting bladeaxis 13 are positioned inclined to each other at an acute angle a sothat the distance 14 (compare FIG. 2) of the cutting blades 11, 12 inthe direction of the imagined window axis 9, i.e., in a paralleldirection of projection 16 to the window edges 6, 7, corresponds to therequired distance 8 of the window edges 6, 7. In the example shown, theinclination angle a is about 5°.

[0029]FIG. 2 shows in detail that in the initial state—i.e., unwornstate—the distance 14 of the cutting blades 11, 12 relative to thecutting blade axis 13 is greater by a dimension than the requireddistance 8 of the window edges 6, 7 (compare FIG. 1) so that the cuttingblades 11, 12 without inclination would stand out by /2 beyond thewindow edges 6, 7 to be machined. By reducing the inclination of windowaxis 9 and cutting blade axis 13 towards each other, the cutting bladedistance 14 in the direction of the window axis 9 is reduced due to ageometric relation: The cutting blade distance in the direction ofwindow axis 9=cutting blade distance 14 in the direction of cuttingblade axis 13•cos α.

[0030] With this initial inclination, the machining of the window edges6, 7 is begun. As wear of the cutting blades 11, 12 increase, theinclination angle a is reduced increasingly towards 0° to compensate forthe wear-related reduction of the cutting blade distance 14 or thecutting tool width. Here, either the inclination of the ball cage 1, theinclination of the cutting blade axis 13 or both may be changed. In theexample shown, the cutting plate of the single-tooth milling cutter 2 isfixed rigidly to the shaft 10 and the inclination of the cutting bladeaxis 13 is changed by inclining the axis of rotation 15 of the shaft 10.Both window edges 6, 7 are machined simultaneously to the exactdimensions resulting in the machining time being reduced in-half, incontrast to the current state of technology, and while keeping thetolerance width over the lifetime of the tool. The wear dimension andthe inclination angle a are adjusted in a way so that the tool 2 is wornby about the time the inclination angle a is reduced to 0°.

[0031] In the embodiment shown in FIG. 3, the window axis 9 runsinclined to the vertical with the window edges 6′, 7′ runninghorizontally in the direction of the thickness of the circumferentialwall 5′ so that the window edges 6′, 7′ are staggered horizontally toone another. As in the example described above, the cutting blade axis13′ is initially inclined at an angle a to the window axis 9′. Withincreasing wear of the cutting tool 2′, the inclination angle a isreduced in a way that both window edges 6′, 7′ positioned horizontallystaggered to each other can be finished simultaneously, i.e., in onestep.

[0032] As indicated in FIG. 1, the work piece or ball cage 1 can beturned in the same rotational direction as the cutting tool 2 so thatthe circumferential surface, in which the window edges 6, 7 are to bemachined and the tool 2 are moved in opposite directions at contact. Dueto this, the tool 2 machines the window surfaces alongside thecircumferential surface of the work piece or the ball cage 1 in regularintervals. Work piece 1 and cutting tool 2 are turned towards each otherin a predetermined rotation ratio of n₁/n₂. If for example six windows 3are to be manufactured alongside the periphery of the ball cage 1, thetool 2 rotates six times as fast as the ball cage 1. As an alternativeto an opposite rotation a synchronous rotation is also possible.

I/We Claim:
 1. Procedure for machining openings in work pieces, inparticular of windows in ball cages for constant velocity joints, withthe following steps: Providing a cutting tool, which rotates around anaxis of rotation having two cutting blades positioned alongside of theaxis of rotation with a distance to one another (11, 12), whichdetermine a cutting blade axis running through both. Supporting a workpiece near the cutting tool in a way that an imagined opening axis (9),which runs through two oppositely positioned opening edges (6, 7) to bemachined in a predetermined alignment to the cutting blade axis, andMachining of the opening edges of the work piece by cutting one openingedge with one cutting blade and the other opening edge with the othercutting blade with both opening edges showing a required distance (8) toone another alongside the opening axis in finished state, characterizedby the following steps: Positioning of the two cutting blades (11, 12)along the cutting axis (13) at a distance to one another (14), which isgreater that the required distance (8) between the opening edges (6, 7),Inclination of the opening axis (9) and the cutting blade axis (13) inan initial position at an acute angle (α) to one another so that thedistance between the cutting blades (11, 12) parallel to the openingaxis (9) is equal to the required distance (8) of the opening edges (6,7), and Reduction of the inclination angle (α) with a wear of thecutting blades (11, 12) so that the cutting blade distance parallel tothe opening axis (9) continues to correspond to the required distance(8) of the opening edges (6, 7).
 2. Procedure according to claim 1 [ischaracterized by inclining] further comprising the step of setting theinclination angle (α) of the opening axis (9) to the cutting blade axis(13) in the initial position [by] at an angle of up to 5°.
 3. Procedureaccording to claim 1 [or 2 is characterized by] further comprising thestep of reducing the inclination angle (α) from the initial position toapproximately 0°, with the cutting blades (11, 12) being totally worn atabout 0°.
 4. Procedure according to [one of claims 1 to 3 ischaracterized by] claim 1 further comprising the step of modifying theinclination angle [of] by repositioning the cutting blade axis (13) [forpositioning] and thereby reducing the inclination angle (α). 5.Procedure according to claim 4 [is characterized by] further comprisingthe step of rigidly joining the cutting blade axis (13) and the axis ofrotation (15) and by modifying the inclination of the axis of rotation(15) for positioning and reducing the inclination angle (α). 6.Procedure according to claim 5 [is characterized by] further comprisingthe step of positioning the cutting blade axis 913) parallel to the axisof rotation (15) of the cutting tool (2).
 7. Procedure according to [oneof claims 1 to 6 is characterized by] claim 1 further comprising thestep of modifying the inclination [of] angle by repositioning the workpiece (1) [for positioning] and thereby reducing [of] the inclinationangle (α).
 8. Procedure according to [one of claims 1 to 7 ischaracterized by] claim 1 further comprising the steps of turning thework piece (1) in the same [or opposite] direction of rotation as thecutting tool (2) so that the circumferential surface of the work piece(1) and the cutting blades (11, 12) are moved opposing [or synchronous]to each other at contact and the cutting blades (11, 12) machineopenings (3) at regular intervals along the circumferential surface. 9.(NEW) Procedure according to claim 1 further comprising the steps ofturning the work piece (1) in the opposite direction of rotation as thecutting tool (2) so that the circumferential surface of the work piece(1) and the cutting blades (11, 12) are moved synchronous to each otherat contact and the cutting blades (11, 12) machine openings (3) atregular intervals along the circumferential surface.
 10. Procedureaccording to [one of claims 1 to 7 is characterized by the] claim 1further comprising the steps of machining [process of] one opening[being performed] with the work piece held in a fixed position (1). 11.Procedure according to [one of claims 1 to 9 is characterized byavoiding the forming of grooves in the opening edges by a subsequentremoval of the cutting tool (2) from the opening at the end of themachining process by] claim 1 further comprising the steps of, aftermachining, increasing the inclination angle (α) to [a certain] an extentand removing the cutting tool from the opening thereby avoiding forminggrooves in the opening edges during removal.
 12. (NEW) A method ofmachining openings in a work piece comprising the steps of: providing acutting tool having two cutting edges, the edges located a firstdistance apart and defining a cutting axis extending through the edges;providing a work piece adjacent to the cutting tool, the work pieceincluding a face in which an opening is to be machined, the openinghaving generally opposed opening edges located a second distance apartand defining an opening axis extending through the opening edges;positioning the cutting tool and the work piece such that the cuttingaxis and opening axis form an acute angle therebetween; rotating thecutting tool about an axis of rotation; and as said cutting tool isrotated about the axis of rotation, advancing the cutting tool into thework piece along an axis substantially normal to the opening axisthereby machining the opening in the work piece.
 13. (NEW) The method ofclaim 12 wherein said positioning step forms the angle at an initialangle of about 5°.
 14. (NEW) The method of claim 12 wherein saidpositioning step forms the angle at an initial angle of not more than5°.
 15. (NEW) The method of claim 11 further comprising the step ofreducing the angle in proportion to wear of the cutting tool.
 16. (NEW)The method of claim 15 wherein said reducing step is achieved by movingthe cutting tool and adjusting the cutting axis relative to the openingaxis.
 17. (NEW) The method of claim 15 wherein said reducing step isachieved by moving the work piece and adjusting the opening axisrelative to the cutting axis.
 18. (NEW) The method of claim 15 whereinsaid reducing step is achieved by moving both the work piece and thecutting tool thereby adjusting the angle therebetween.
 19. (NEW) Themethod of claim 12 further comprising the step of positioning thecutting tool such that the cutting axis is parallel to the axis ofrotation.
 20. (NEW) The method of claim 12 further comprising the stepof positioning the cutting tool such that the cutting axis is notparallel to the axis of rotation.
 21. (NEW) The method of claim 15wherein the step of reducing is done such that the cutting axis and theopening axis are generally parallel when the cutting tool issubstantially totally worn.
 22. (NEW) The method of claim 12 whereinsaid first distance is defined as being greater than said seconddistance.